Method for removing metals from a solution

ABSTRACT

The present invention is a method to remove metals from solutions by precipitating the metals and adding cellulosic fiber to the solution. The precipitates attach to the cellulosic fibers to form products. The products may be removed from the solution by gravity separation techniques or by filtration. The removed products may be dewatered and incinerated. The method provides a simple and effective technique for removing low concentrations of metals from high volume solution streams.

FIELD OF THE INVENTION

The present invention is a method for removing metals from a solution.More particularly, the present invention embodies an improved approachfor removing precipitates containing such metals from an effluent.

BACKGROUND OF THE INVENTION

Discharges of metals into the environment are a major problem worldwide.Metal discharges severely damage the environment, being responsible eachyear for the contamination of water resources and destruction of plantand animal life.

Metal discharges into surface and ground water resources (e.g., streams,rivers, ponds, lakes, and aquifers) pose the greatest risk to wildlifeand human health. Such discharges may be either manmade, such asdischarges by industrial facilities, or natural, such as water runofffrom caves and mines. Treatment of contaminated surface and ground waterresources is complicated not only by the large quantities of water butalso by the dilute concentrations of metals contained in the resources.

Existing methods to remove metals from aqueous solutions are poorlysuited to remove dilute concentrations of metals from large quantitiesof water to achieve the purity levels mandated by state and federallaws. Existing metal removal methods include the steps of precipitatingthe metals and removing the precipitates from the solution by filteringor by density separation techniques, such as by settling.

The conventional filtering techniques are not only uneconomical but alsocan fail to remove a significant portion of the precipitates in manyapplications. The dilute (e.g., parts per million) concentrations ofmetals in surface and ground water resources cause very small metalprecipitates to form. As will be appreciated, such precipitates can forma thick filter cake or gelatinous mass on the filter causing a largepressure drop across the filter and a small filter flux. The resultingflux is typically too low to handle economically the large amounts ofcontaminated water. Many resources contain particulate matter, otherthan the precipitates, that further impedes the filtering step.

Another conventional technique to remove precipitates, is by densityseparation, which is also not economical in most cases. The most commondensity separation technique for large quantities of water is a settlingpond, where metal precipitates settle out of solution. Settling pondsare typically undesirable as they require large land areas that areoften not available, create a highly toxic sludge in the pond bottomthat is often difficult to dispose of, and often fail to attain desiredlevels of purity in the pond overflow.

Other techniques to remove metal contaminants from surface andgroundwater resources require expensive components and/or otherwiseraise other operational complications.

Therefore, there is a need for a process to inexpensively remove metalsfrom surface and ground water resources having low concentrations ofmetals.

SUMMARY OF THE INVENTION

In a preferred embodiment, the present invention relates to a novelmethod for remediation of feed solutions containing a metal. In a firststep, a feed solution is provided containing a metal precipitate. In asecond step, discrete fibers are dispersed in the feed solution. Theprecipitate attaches to a discrete fiber to form a product. The productis removed from the feed solution to form a treated solution and arecovered product.

The feed solution may have high rates of flow of more than about 500gallons/minute. The feed solution may also have low metal concentrationsless than about 50 parts per million by volume. The metals removed bythe present invention may include aluminum, arsenic, beryllium, boron,cadmium, chromium, fluorine, nickel, selenium, vanadium, lithium,molybdenum, barium, lead, mercury, silver, copper, zinc, manganese, ironcompounds thereof and mixtures thereof.

The precipitate preferably includes hydroxides, silicates, sulfides,xanthates, phosphates, carbonates, cellulose-derivatives, and mixturesthereof. More preferably, the precipitate includes hydroxides,silicates, carbonates, and mixtures thereof. In one embodiment, theprecipitate is formed by precipitating the metal from the feed solutionusing a precipitant. The precipitant preferably includes a hydroxide,silicate, sulfide, xanthate, phosphate, carbonate, hydroxyethylcellulose, and mixtures thereof. In an alternate embodiment, thediscrete fibers may include the precipitant.

In one embodiment, the product is removed from the feed solution byfiltering. The filtering step may be preceded by a thickening step. Inan alternate embodiment, the product is removed from the feed solutionby a density separation method.

After product removal, the treated solution preferably has a metalconcentration that is less than the maximum concentrations fordischarges into water resources under regulations promulgated by theEnvironmental Protection Agency.

The recovered product may be dewatered. The recovered product preferablyhas a water content less than about 90% by weight before dewatering. Thedewatered product preferably has a water content less than about 30% byweight. The dewatered product may be combusted.

In an alternate embodiment, a method is provided for concentrating themetals in the feed solution. In a first step, the metals areprecipitated from the feed solution. In a second step, discrete fibersare dispersed in the feed solution to form the product. The product isallowed to collect in a portion of the feed solution by densityseparation techniques.

Various embodiments of the present invention offer numerous advantagesover existing methods and apparatuses. First, one embodiment of thepresent invention provides an inexpensive and simple method to purifylarge quantities of contaminated water at high flow rates. The productof the fibers and precipitates may be selected such that the product issubstantially larger than the precipitates alone. The product sizeallows the present invention to employ larger filter pore sizes andtherefore higher filter fluxes than is possible with conventionalpurification methods. The product size may be selected such that otherentrained particulate matter is smaller than the product and passesthrough the filter while the product does not.

Second, another embodiment of the present invention may economicallypurify solutions having low metal concentrations. Unlike conventionalmethods, which produce smaller metal precipitates for lower metalconcentrations, the present invention employs fibers to collect themetal precipitates before removal. The product of the fiber and metalprecipitates may then be rapidly and easily removed by any number ofmethods known in the art.

Third, in another embodiment of the present invention, high settlingrates of product can be attained by appropriate selection of productsize and the use of settling aids. This improvement permits the productto be removed more rapidly by flocculation, thickening, and filtrationof the feed solution, than would otherwise be possible with theprecipitate alone.

Fourth, recovered product of the present invention may have a muchsmaller volume than the sludge produced by conventional purificationmethods. Thus, subsequent handling and disposal of such materials isrelatively more simple. For example, the recovered product may beincinerated to an even smaller volume than the recovered product. Thecinders from incineration may be disposed of or further treated torecover the metals contained in the cinders. The disposal of cinders ismuch easier and less expensive than the cost to dispose of the sludge orfiltrate produced by conventional purification methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow schematic of the subject invention, illustrating theuse of fibers to remove metal precipitates from solution.

DETAILED DESCRIPTION

A first embodiment of the present invention is a method for remediationof a feed solution containing a metal. The metal is contained in aprecipitate. Discrete fibers are dispersed in the feed solution to forma product including a fiber and the precipitate. The product is removedfrom the feed solution to form a treated solution and a recoveredproduct.

The feed solution may be any liquid containing a metal. Preferably, thefeed solution is aqueous. More preferably, the feed solution is aportion of a stream, river, pond, lake, or any other naturally occurringor manmade aqueous stream or reservoir. The process of the presentinvention can be conducted in a channel, reservoir, or other type ofcontainer. Preferably, the feed solution is provided for remediation ina channel, such as a sluice box, or in a stirred tank.

A preferred embodiment of the present invention purifies a feed solutionhaving a high rate of flow. The flow rate of the feed solution ispreferably greater than about 10 gallons per minute, more preferablygreater than about 100 gallons per minute, and most preferably greaterthan about 500 gallons per minute. Such flow rates are in excess of theamount of water that can be readily and effectively treated byconventional methods.

The metal to be removed from the feed solution preferably is atransition element (an element from Groups IB through VIIB and GroupVIII of the Modern Periodic Table of the Elements), an alkali metal(Group 1A), an alkaline earth metal (Group 11A), aluminum, boron, lead,arsenic, selenium, fluorine, compounds thereof, or mixtures thereof.Most preferably, the metal is aluminum, arsenic, beryllium, boron,cadmium, chromium, fluorine, nickel, selenium, vanadium, lithium,molybdenum, barium, lead, mercury, silver, copper, zinc, iron,manganese, compounds thereof, or mixtures thereof.

The present invention is particularly suited to the removal of low metalconcentrations from the feed solution. Surprisingly, the presentinvention may remove significant portions of metal from feed solutionshaving metal concentrations less than about 50 mg/l. The presentinvention removes preferably at least about 75, more preferably at leastabout 85, and most preferably at least 90% by weight of metals from afeed solution having a concentration less than about 50 mg/l.

The metal may be in the form of either an element or a metal-containingcompound (hereinafter collectively referred to as "metal"). In oneembodiment of the present invention, the metal is in the feed solutionin the form of a precipitate. As used herein, "precipitate" refers toany compound containing the metal that is insoluble in the solution. Foraqueous solutions, the metal-containing compound should be waterinsoluble. Preferably, the precipitate is a hydroxide, silicate,sulfide, xanthate, phosphate, carbonate, cellulose-derivatives, ormixtures thereof. More preferably, the precipitate is environmentallybenign. Most preferably, the precipitate is a hydroxide, silicate,carbonate, or mixtures thereof.

In an alternate embodiment of the present invention, the metal is in aform that is soluble in the solution and is precipitated from the feedsolution to form the precipitate. "Precipitated" or "precipitating"refers to any process that causes a dissolved metal to form aprecipitate. Preferably, such a process includes a chemical reactionbetween the soluble metal and a precipitant that produces a precipitate.

A precipitant may be introduced to the feed solution before, concurrentwith, or after the discrete fibers are dispersed in the feed solution.As used herein, "precipitant" refers to any element or compound capableof forming a precipitate with the metal in the feed solution.Preferably, the precipitant is selected such that the precipitant andthe precipitate containing the metal are each environmentally benign.More preferably, the precipitant is a hydroxide, silicate, sulfide,xanthate, phosphate, carbonate, hydroxyethyl cellulose, or mixturesthereof. Most preferably, the precipitant is CaCO₃, Na₂ CO₃, Ca(OH)₂,Na₂ SiO₃, CaS, NaHS, H₃ PO₄, CaH₄ (PO₄)₂, or mixtures thereof.

The precipitant may be contacted with the feed solution either as a partof the discrete fibers or as a separate additive, as desired. In thecase of the precipitant as part of the fiber, the precipitant may beattached to the discrete fibers by any means known in the art to formfunctionalized fibers. The functionalized fibers may form themetal-containing precipitate either directly on the discrete fibers orin the feed solution. For functionalized fibers, the precipitant ispreferably a phosphate, xanthate, or hydroxyethyl cellulose.

The desired concentration of the precipitant in the feed solution isgreat enough to obtain acceptable reaction with metal in the feedsolution. The precipitant is preferably present in the feed solution inat least stoichiometric amounts relative to that amount of metal in feedsolution to be removed. More preferably, the precipitant is at leastabout 200% of the stoichiometric amount relative to the amount of metalin the feed solution to be removed.

The time provided for reaction between the precipitant and the metal inthe feed solution between introduction of the precipitant and removingproduct from the feed solution is sufficient for substantial completionof the reaction. Preferably, the residence time for substantialcompletion of the reaction ranges between about 1 to about 120 minutes,more preferably between about 1 to about 30 minutes, and most preferablybetween about 1 to about 10 minutes.

As noted above, a discrete fiber is dispersed into the feed solution toform a product with the precipitate. "Discrete fibers" refer to fibersthat are not attached to one another. The fibers are preferably composedof cellulose, glass, plastic, cotton, or wool. More preferably, thefiber is composed of cellulose. "Cellulose" refers to a naturalcarbohydrate polymer having anhydroglucose units joined by an oxygenlinkage to form long molecular chains. For example, the discrete fibersmay be in the form of shredded paper.

The fibers can be of varying sizes and shapes and typically areelongated in at least one dimension. For example, a paper fiber is amaterial having a size of less than about 3.0 mm, more preferably lessthan about 2.5 mm, and most preferably less than about 2.0 mm.Preferably, the median size of the discrete fibers is less than about2.5 mm. The size and median size of the discrete fibers is measuredbased on the longest dimension of the discrete fibers. As will beappreciated, the size of the discrete fibers may be selected either toyield a desired settling rate of product in the feed solution or topermit the use of a desired filter pore size to remove the product fromthe feed solution. The desired size distribution of fibers can dependupon the application. Both broad and narrow size distributions arewithin the scope of the invention. Typically, the size distribution ofthe discrete fibers will be directly proportional to the sizedistribution of the product. Generally, the size of the product is notsignificantly different from the size of the fiber from which theproduct originated.

The settling rate of product may be further increased to a desired rateby the use of settling aids with the fibers. As used herein, a "settlingaid" refers to a substance that attaches to the product and causes thespecific gravity of the product and the settling aid to be greater thanthe specific gravity of the product alone. Preferred settling aids aresand and magnetite.

In one embodiment of the present invention, the discrete fibers may bedispersed in the feed solution as part of an aqueous slurry. In analternative embodiment, dry discrete fibers may be added directly to thefeed solution. The addition of the discrete fibers to the feed solutionas a slurry allows for more rapid dispersion of the fibers relative tothe addition of dry discrete fibers paper directly to the feed solution.

The volume of the discrete fibers dispersed in the feed solution canvary depending on process conditions and is selected so as to achieveacceptable remediation. Preferably, the concentration of the discretefibers dispersed in the feed solution is from about 10 to about 1000,more preferably from about 50 to about 800, and most preferably fromabout 100 to about 500 mg/l.

The dispersion of the discrete fibers in the feed solution may beaccelerated by agitation. The agitation may be induced passively bybaffles or actively by mechanical means, such as an impeller in astirred tank.

It has been found that by operation of the present invention, thediscrete fibers attach to the precipitates to form products. Theattachment between the precipitate and the fiber occurs whether theprecipitant is attached to the discrete fibers or added to the feedsolution separately from the fibers.

The time between the introduction of discrete fibers into the feedsolution and the removal of the product from the feed solution issufficient to achieve acceptable precipitation of metals from thesolution. Preferably, the time is sufficient for a majority, morepreferably at least 75%, and most preferably at least 95% of theprecipitate to form a product with the discrete fibers.

The process of the invention can further include removing the productfrom the feed solution to form a treated solution and a recoveredproduct. In one embodiment of the present invention, the removing stepincludes filtering the feed solution to remove the product As usedherein, "filtering" includes screening as well as filtering. In thefiltering step, the feed solution is filtered to form the treatedsolution as the filtrate and the recovered product as the cake. Thefiltration of the feed solution may be accomplished by any continuous ornon-continuous filters known in the art. A preferred filter iscontinuous. The more preferred filters are rotary drum and rotary diskfilters and the most preferred filters are rotary drum filters, such asstring filters and rotary belt filters.

The filter pore size is a function of the size distribution of thediscrete fibers and the size distribution of other particulate matter inthe feed solution. Thus, the filter pore size may be selected based uponthe size distribution of the discrete fibers.

The filter pore size is preferably sufficient to retain substantiallyall of the discrete fibers while passing substantially all of the feedsolution and other particulate matter entrained therein. To removeentrained particulate matter larger than the discrete fibers, it may bedesirable to have located upstream screens or secondary filters thathave a pore size sufficient to remove the entrained particulate matterbut large enough to pass substantially all of the discrete fibers.

The filter pore size desirably retains at least about 80%, moredesirably at least about 90%, and most desirably at least about 95% ofthe discrete fibers. To retain the desired amount of the fibers, thefilter pore size is desirably smaller than the longest dimension of thatportion of the size distribution of the fibers that is sought to berecovered. Preferably, the filter pore size ranges from no more thanabout 2.0, more preferably no more than about 1.0 and most preferably nomore than about 0.5 mm.

As will be appreciated, density separation methods may be employed toremove the product from the feed solution. By way of example, theproduct may be allowed to settle under gravity in settling ponds. Asstated above, the size distribution of the fibers may be selected toyield a desired settling rate of the product in the feed solution. Theupper portion of the feed solution may be removed after settling of theproduct is completed. Other methods to remove the product includeclassifiers, centrifuges, and so forth.

In some embodiments, the feed solution is contacted with a flocculant toconcentrate the product in the feed solution or to assist in formationof a product between a fiber and a precipitate. As used herein,"flocculant" refers to any substance that increases the cohesive forcesamong the discrete fibers or among fibers and precipitates in the feedsolution. The flocculant assists in formation of product or removal ofthe product from the feed solution by aggregating the product intodiscrete domains in the feed solution. The aggregated product morequickly settles under gravity to the bottom of the feed solution thandoes the product in the absence of the flocculant.

The flocculant may be a polyacrylamide. For example, a suitablepolyacrylamide flocculant is sold under the trademark "PERCOL 351".

The desired concentration of flocculant in the feed solution is afunction of the concentration of the product (e.g., the concentration ofthe discrete fibers introduced into the feed solution) in the feedsolution. Preferably, the flocculant concentration is less than about 1mg/l and typically is from about 0.1 to about 1 mg/l.

In a further alternative embodiment, which may be used in combinationwith flocculation, the feed solution, after flocculation, may be treatedby thickening techniques known in the art to produce an overflowsolution and slurry. Thickening facilitates later filtration by reducingthe volume of solution that needs to be filtered to remove the product.Thickening concentrates the product and the discrete fibers in a lowerportion of the flocculated solution, thereby permitting an upper portionto be removed as the overflow solution. In this embodiment, the slurryis preferably no more than about 1/20, more preferably no more thanabout 1/50, and most preferably no more than about 1/100 of the volumeof the feed solution. The overflow solution preferably contains lessthan about 30% of product, more preferably contains less than about 20%of product, and most preferably is substantially free of product.

The treated solution formed from the process as broadly described abovepreferably contains less than the concentrations allowed by applicablelocal, state or federal regulations. For example, the U.S. EnvironmentalProtection Agency establishes allowable concentrations for variousmetals of the present invention for agricultural and domestic uses. Suchstandards are hereby incorporated by reference.

The recovered product may be conveniently disposed of by severaltechniques. In one embodiment, the recovered product is dewatered.Before dewatering, the recovered product has a water content of morethan about 50%, more typically more than about 75%, and most typicallymore than about 90% by weight. The dewatered product has a water contentless than about 30%, more preferably less than about 20%, and mostpreferably less than about 10% by weight. The recovered product may bedewatered by any means known in the art, including compaction or drying.

In another embodiment, the recovered product and particularly, dewateredproduct may be incinerated to produce cinders and a waste gas. The wastegas may be scrubbed with the overflow solution to remove deleteriousmaterials, including metals. The overflow solution after scrubbing(e.g., the scrubbing solution) is recycled. Before recycle, it ispossible to recover the metals from the scrubbing solution by standardtechniques. The cinders may be disposed of or recycled, as desired.

In an alternative embodiment of the present invention, the metals may beconcentrated in a solution by precipitating the metal from the solutionto form a precipitate; dispersing discrete fibers in the solution toform a product containing a discrete fiber and the precipitate; andallowing the product to collect in a portion of the solution by densityseparation techniques.

This embodiment is particularly applicable to large, stationary bodiesof water, such as lakes, reservoirs and ponds, to concentrate metals inthe bottom sediments of the body of water in a form that is less harmfulto aquatic life. It is often not practical to remove the settled productfrom the bottom sediments. The removal cost may be prohibitive due tothe cost to remove the bottom sediments, typically by dredging, and todispose of the removed material.

FIG. 1 depicts a preferred embodiment of the present invention asapplied to water runoff from a mine (hereinafter called "acid minedrainage"). Discrete fibers 6 are introduced into feed solution 4 by anymeans known in the art to form a fiber-containing solution 7.

A precipitant 10 and, in some cases, pH adjustor 8 may be contacted withfiber-containing solution 7 to form a precipitate-containing solution11. This step is desired if the metal is in a water soluble form andmust be precipitated. The pH adjustor 8 may be an acid or base, asdesired. In some applications, the pH adjustor 8 is unnecessary since pHadjustment is provided by the precipitant. The pH is adjusted to providethe desired conditions in precipitate-containing solution 11 forprecipitant 10 to react with the metal to form a precipitate.Preferably, pH adjuster 8 is an environmentally benign compound. Foracid mine drainage, to make the pH more basic the preferred pH adjustor8 is a hydroxide, such as calcium hydroxide, or carbonate, such ascalcium carbonate and/or sodium carbonate. To make the pH more acidic,the preferred pH adjustor 8 is sulfuric acid or carbonic acid. Thepreferred pH in precipitate-containing solution 11 ranges from about 4to about 11 and more preferably from about 6 to about 8.5.

Precipitate-containing solution 11 may be contacted with flocculant 16to concentrate the product in flocculated solution 14. In flocculatedsolution 14, the metal-containing precipitate attaches to discretefibers 6 to form a product in the precipitate-containing solution 11.Flocculated solution 14 may be treated by any thickener known in the artto produce an overflow solution 18 and slurry 20.

Overflow solution 18 may be used to scrub waste gas 22 in a conventionalscrubber. The portion of overflow solution 18 that is not used to scrubwaste gas 22 may be added to treated solution 24.

Recovered product 12 may be dewatered. Dewatered product 26 may beincinerated to form waste gas 22 and cinders 28. Waste gas 22 may bescrubbed with overflow solution 18 to remove deleterious materials,including metals. The scrubbing solution 30 may be added to feedsolution 4 for purification. Cinders 28 may be disposed of or recycled,as desired.

EXAMPLE 1

A series of tests were run to illustrate that by using paper fiber, atype of fiber, sludge settling, filtering and compaction is improved.Some of the tests were performed on an acid mine drainage (AMD). Ananalysis of the AMD is shown below in Table 1.

                  TABLE 1                                                         ______________________________________                                        Analysis of Acid Mine Drainage                                                         Concentration           Concentration                                Component                                                                              (mg/L)       Component  (mg/L)                                       ______________________________________                                        Mg       401          Cd         .35                                          Ca       329          B          0.23                                         Mn       170          Ba         0.14                                                               Pb         0.14                                         Mn       130          Li         0.05                                         Fe       128          Au         <0.05                                                              Se         <0.05                                        Zn       104          As         0.03                                         Na       91                                                                   K        14           Co         0.02                                         Si       6.8          V          0.02                                         Al       3.1          Be         0.008                                        Cu       2.1          Ge         <0.008                                       Ni       1.4          Cr         0.004                                        P        1.1          Mo         <0.003                                                             Hg         <0.002                                       Sr       0.38                                                                 ______________________________________                                    

In each experiment in Table 2, the AMD sample was spiked to 25 or 50mg/L Cu with CuSO₄ and diluted (1 part AMD to 3 parts demineralized H₂O).

The paper fiber, as a 2 weight percent slurry, was prepared by shreddingnewspaper in water using a blender. The ash content of the sample wasless than 2%.

The tests were conducted in baffled 600 to 1000 ml beakers using gentlemixing at room temperature (22° to 24° C.) for 7 to 10 minutes. Apolyacrylamide flocculant was used in some of the experiments as notedin Table 2. The polyacrylamide flocculant employed is sold under thetrademark "PERCOL 351". After flocculation, the precipitate and/orfibers were settled, decanted and the thickened slurry was filteredthrough 48 or 65 mesh screens, or paper towel filter.

The pH was maintained at 9.1 with 0.73 grams of Na₂ CO₃. Hydrogenperoxide was added in the amount of 30 mg to oxidize manganese to MnO₂.The solution temperature was maintained at 23° C. for 10 minutes.

Other experimental conditions or procedures are described in Table 2.

As shown below in Table 2, with paper fiber added, the precipitatesettled roughly three times faster and was filterable through a loosepaper fiber filter. The supernatant solution and filtrate were crystalclear. In those tests where no paper fiber was employed, finerprecipitates passed through the filter to produce a less pure solutionthan was obtained with paper fiber. Additionally, the volume of thepressed cake and paper fiber is about a tenth as much as the centrifugedprecipitate when no paper fiber was employed (which is analogous to thethickened sludge in a settling pond of a conventional purificationprocess).

                                      TABLE 2                                     __________________________________________________________________________    The Effect of Paper Fiber on the Separation of Heavy Metals Precipitate       Test Objective       Test Conditions     Results                              __________________________________________________________________________    Precipitating of Cu, Zn, Mn, Fe                                                                    Paper fiber = 0.2 g Settling rate = 0.7 ft/min,                                                   thickened slurry =                   from diluted AMD with Na2CO3                                                                       Precipitate separated from solution                                                               50 ml in 10 min.                     plus paper fiber to  filtration through 7.5 cm paper fiber                                                             clear supernatant solution           determine effect on  filter at 1" Hg vacuum. THe moist cake                                                            Filtration = 65 ml/20 sec (1.1                                                gpm/sq./ft.)                         thickening and filtration                                                                          was pressed, dried at 85 C., and ignited                                                          clear filtrate                                            700 C.              Precipitation and fiber                                                       (pressed):                                                                    thickness = 0.1 mm                                                            vol ˜ 0.7 cc                                                            moist wt = 1.83 g                                                             dry wt = 0.40 g, (21.9%)                                                      solids)                                                                       ignited wt = 0.18 g                  Precipitating of Cu, Zn, Mn, Fe                                                                    Paper fiber = none  Settling rate = 0.2 ft/min,                                                   thickened slurry =                   from diluted AMD with Na2CO3                                                                       Precipitate separated from solution                                                               55 ml in 10 min.                     without paper fiber to                                                                             filitration through 7.5 cm paper fiber                                                            supernatant solution contained       determine precipitate filterability.                                                               filter at 1- Hg vacuum.                                                                           suspended fibers                                                              Filtration = fines passed                                                     through filter                       Precipitation of Cu, Zn, Mn, Fe                                                                    Paper fiber = none  Settling rate = 0.3 ft/min,                                                   thickened slurry =                   from diluted AMD with Na2CO3 without                                                               Precipitate separated from solution                                                               40 ml in 10 min.                     paper fiber to       centrifuge operation at 1000 rpm for                                                              supernatant solution contained       determine how much sludge is formed.                                                               min.                suspended fines                                                               Centrifuged sludge volume = 9        __________________________________________________________________________                                             cc                               

EXAMPLE 2

The tests in Table 3 below were done according to the same procedures asExample 1 with the exceptions enumerated in Table 3 and the preparationof the solutions. For the copper sulfide precipitation tests, solutionswere made up using reagent grade CuSO₄ and Na₂ SO₄ salts.

The data from the tests in Table 3 show the applicability of paper fiberas a settling and filtration aid for precipitating Cu as hydroxide,silicate, sulfide, and xanthate and Cu, Zn, Fe and Mn (which is oxidizedto precipitate out MnO₂) as hydroxides or carbonates.

                                      TABLE 3                                     __________________________________________________________________________    Test Objective Test Conditions          Results                               __________________________________________________________________________    Heavy metal    Feed soln = 1.00 liter AMD                                                                             Precipitate and fiber settled                                                 rapidly                               precipitation  Mixture: Paper fiber = 0.23 g + Ca(OH)2 =                                                              Thickened slurry (200 cc)                                                     filtered in - 3 min                   with Ca(OH)2   0.58 g mixed lime and paper fiber for                                                                  giving a slime cake                   using paper                                                                   15 min.                                                                       fiber as settling                                                                            pH = 8.9 adjusted with slight amount Ca(OH)2                   and filter aid H2O2 = added 30 mg after pH adjust to 8.9                                     Temp = 22 C., Time = 15 min                                                   "PERCOL 351" = 0.5 mg                                                         Solid/Liquid Separation = settled, and filtered                               through 65 mech, 7.5 cm screen at 1"                                          vacuum                                                         Cu precipitation                                                                             Feed soln = 50 mg/L Cu + 1.3 g/l Na2SO4,                                                               Gelatinous type mixture               as silicate    2.9, 1.00 liter          Poor separation through 65 mesh                                               screen                                with paper     Mixture - Paper fiber = 0.2 g                                  fiber as settling                                                             Na2SiO3.Na2) soln = 0.3 ml 40-42 Be                                           and filter aid soln (- 150 mg)                                                               pH = 7.8 with Ca(OH)2 or H2SO4                                                Temp = 22 C., Time = 5 min                                                    "PERCOL 351" = 0.5 mg                                                         Solid/Liquid Separation = Settled and filtered                                through 7.5 cm, 65 mesh screen at 1"                                          vacuum                                                         Cu precipitation as                                                                          Feed soln = 50 mg/L Cu + 1.3 g/l Na2SO4,                                                               Precipitate and fiber settled                                                 rapidly                               sulfide with paper                                                                           2.9, 1.00 liter          Very slight H2S odor                  fiber as settling                                                                            Mixture - Paper fiber = 0.2 g                                                                          Screened OK                           and filter aid                                                                CaS = 90 mg                                                                   Activated carbon = 110 mg powder F-                                                          400                                                                           pH = 8.0 with Ca(OH)2                                                         Temp = 22 C., Time = 6 min                                                    "PERCOL 351" = 0.5 mg                                                         Solid/Liquid Separation = Settled and                                         filtered through 7.5 cm, 65 mesh screen                                       at 1" vacuum                                                   Cu precipitation                                                                             Feed soln = 50 mg/L Cu + 1,3 g/L Na2SO4,                                                               Precipitate and fiber settled                                                 rapidly                               as zanthate    pH 2.9, 1.00 liter       Very slight xanthate odor             with paper     Mixture: Paper fiber = 0.23 g                                                                          Did not appear to "screen"  as                                                well as CaS/AC                        fiber as settling                                                                            "KEX" = 280 mg                                                 and filter aid pH = 6.8 with Ca(OH)2                                                         Temp = 22 C., Time = 8 min                                                    "PERCOL 351" = 0.3 mg                                                         Flocculant = 0.5 mg "PERCOL 351"                                              Solid/Liquid Separation = thickened and                                       filtered through 7.5 cm, 65 mesh                                              screen at 1" vacuum                                            Cu sulfide     Feed soln = 50 mg/L Cu + 1.3 g/L Na2SO4,                                                               Settled poorly, added another 0.5                                             mg "PERCOL                            precipitation  pH = 2.9, 1 liter        351" to flocculate, then solids                                               settled                               from CuSO4 +   Mixture: NaHS added = 66 mg tech flake                                                                 rapidly                               NaSO4 soln     Paper fiber = 0.2 g      Screened rapidly                      using NaHS     "PERCOL 351" = 0.5 mg    Comment: Flocculant best added                                                after                                 and paper fiber                                                                              pH = 7.2 with Na2CO3     neutralization                                       Temp = 22 C., Time = 10 min                                                   Flocculant = 0.5 mg "PERCOL 351"                                              Solid/Liquid Separation = thickened and                                       filtered through 7.5 cm, 65 mesh                                              screen at 1"vacuum                                             Cu sulfide     Feed soln = 50 mg/L Cu + 1.3 g/L Na2SO4,                                                               Settled poorly, supernate =                                                   brownish                              precipitation  pH 2.9, 1.00 liter       (colloidal CuS)                       from CuSO4 +   Mixture: NaHS = 66 mg tech flake                                                                       Comment: Best add NaHS first then                                             adjust pH                             Na2SO4 soln using NaHS                                                                       Paper fiber = 0.2 g                                            and paper fiber                                                                              Na2CO3 = 0.37 mg                                                              pH = 7.2                                                                      Temp = 22 C., Time = 10 min                                                   Flocculant = 0.5 mg "PERCOL 351"                                              Solid/Liquid Separation = thickened and                                       filtered through 7.5 cm, 65 mesh                                              screen at 1" vacuum                                            Cu sulfide     Feed soln = 50 mg/L Cu + 1.3 g/L Na2SO4,                                                               Settled rapidly                       precipitation from                                                                           pH 2.9, 1.00 liter       Filtered OK, clear filtrate           CuSo4 + Na2SO4 Mixture: NaHS = 66 mg tech flake                               soln using NaHS                                                                              Paper fiber = 0.2 g                                            and paper fiber                                                                              pH = 7.1 with Na2CO3                                                          Temp = 22 C., Time = 5 min                                                    Flocculant = 0.5 mg "PERCOL 351"                                              Solid/Liquid Separation = thickened and                                       filtered through 7.5 cm, 48 mesh                                              screen at 1" vacuum                                            Cu Sulfide   STEP NO. 1                 Assays (mg/L)                                                                            Cu Zn Mn Fe                precipitation from soln                                                                    Feed soln = Cu-spiked AMD, Feed soln  23 25 32 14                using NaHS and paper                                                                       1.00 liter                 Treated soln                                                                             0.6                                                                              24 31 11                fiber - Two stage                                                                          Mixture - NaHS = 70 mg tech flake                                                                        % precipitated                                                                           97 <10                                                                              <10                                                                              21                precipitation first                                                           Paper fiber = 0.2 g                     Settled rapidly                       with NaHS at pH 5                                                                            pH = 5.4 with 140 mg Na2CO3                                                                            Filtered OK, clear filtrate           to precipitate Temp = 22 C., Time = 5 min                                     Cu, then with  Flocculant = 0.5 mg "PERCOL 351"                               Na2CO3 to precipitate                                                                        Solid/Liquid Separation = thickened and                        Zn, Fe, and Mn at pH 8.4                                                                     filtered through 7.5 cm, 48 mesh                                              screen at 1" vacuum                                                           STEP NO. 2               Assays (mg/L)                                                                            Cu Zn Mn Fe                               Feed soln = NaHS filtrate from Step No. 1                                                              Feed soln (step                                                                          23 25 32 11                               Paper fiber = 0.2 g      NaHS filtrate (step                                                                      0.6                                                                              24 31 11                               pH = 8.4 with 140 mg Na2CO3                                                                            Treated soln (step                                                                       <0.1                                                                             0.9                                                                              22 <0.5                             Temp = 22 C., Time = 7 min                                                                             % precipitated                                                                           >99                                                                              96 31 95                               Flocculant = 0.5 mg "PERCOL 351"                                                                       (total for steps                                     Solid/Liquid Separation = thickened and                                                                1 and 2):                                            filtered through 7.5 cm, 48 mesh                                                                       Settled rapidly                                      screen at 1" vacuum      Filtered OK, clear filtrate           Cu sulfide     Feed soln = diluted, Cu spiked AMD                                                                     Precipitate flocculated BUT                                                   settled slowly                        precipitation  NaHS added = 70 mg/L     Filtered OK through towel filter                                              - some fines                          without paper fiber                                                                          Paper fiber = none       in filtrate                                          pH = 5.5 with Na2CO3     Comment: appears paper fiber                                                  collects sulfide                                     Temp = 22 C., Time = 7 min                                                                             precipitate and makes settling                                                and filtering                                        Flocculant = 0.5 mg "PERCOL 351"                                                                       better                                Mn precipitation                                                                             Feed soln = diluted, Cu spiked AMD                                                                     Assays (mg/L)                                                                            Cu Zn Mn Fe                from           H2O2 added = 1.8 mg per mg Mn                                                                          Feed soln  23 26 32 15                spiked AMD using                                                                             Paper fiber = 0.2 g/L as slurry                                                                        Treated soln                                                                             <0.5                                                                             0.6                                                                              5.0                                                                              <0.2              H2O2 to oxidize                                                                              Sand = 0.2 g/L, -48 mesh % precipitated                                                                           >97                                                                              98 84 >98               Mn to MnO2 at pH 8.5                                                                         pH = 8.6 with Na2CO3     The fiber and precipitate settled                                             rapidly and                                          Temp = 22 C., Time = 12 min                                                                            filtered OK, clear filtrate.                         Flocculant = 0.5 mg "PERCOL 351"                                                                       Reagent addition (lb per 1000                                                 gal):                                                Solid/Liquid Separation = thickened and                                                                5.5 Na2CO3, 0.5 H2O2, 1.7 paper                                               fiber,                                               filtered through 7.5 cm, 48 mesh                                                                       1.7 sand, 0.004 flocculant                           screen at 1" vacuum                                            Mn precipitation from                                                                        Feed soln = diluted, Cu spiked AMD        % Pre-               simulated AMD by                                                                             Feed soln assay (mg/L) = 23 Cu, 26 Zn, 15                                                              Assays min mg/L                                                                                cipitated            contacting with                                                                              31 Mn; pH 2.9            Feed soln  31                         precipitated MnO2                                                                            MnO2 added = -200 mg/L MnO2 as slurry                                                                  Treated soln                                                                         10  23    26                                  Paper fiber = 0.2 g/l           30  21    32                                  Sand = 0.2 g/L -48 mesh  Settled fast, but some fines                                                  suspended                                            pH = 86 with Na2CO3      Filtered well, clear filtrate                        Temp = 22 C., Time = 8 min                                                    Solid/Liquid Separation = thickened and                                       filtered through 7.5 cm, 48 mesh                                              screen at 1" vacuum                                            Reaction of xanthated                                                                        Xanthating - Paper fiber = 5.0 g, H2O = 175                                                            Assays, mg/L                                                                             Mn Zn Cu Fe                paper fiber with                                                                             CS2 = 10 g, Ethanol = 6.0 g                                                                            Feed soln  30 24 24 13                diluted AMD                                                                   Contact: Temp = 23 C., Time = 18 hr                                                          Treated soln             28         4.6                                                                              <0.1                                                                             2.8                                 Diluted AMD = 250 ml AMD + 25 mg Cu to 1000                                                            Fiber and precipitate = 2.23 g                                                moist                                                ml                       floc (e.g., the flocculated                                                   precipitate)                                         Paper fiber (xanthated) = 8,2 g, pH rose                                                               settled OK, light floc tended to                                              flow                                                 2.8 to 7.1               Filtered OK                                          Temp = 22 C., Time = 9 min                                                    Flocculant = 0.5 mg "PERCOL 351"                                              Solid/Liquid Separation = settled, and filtered                Treat diluted AMD                                                                            Impregnated Peat mixture: Peat = 7.73 g,                                                               Assays, mg/L                                                                             Mn Zn Cu Fe                with impregnated                                                                             "DEMPA" =                Feed soln  30 24 24 13                DEHP(Ca) - Peat.                                                                             5.08 g, 6.2 acetone, mixed and                                                                         Treated soln, 10                                                                         27n                                                                              16 3.5                                                                              <0.1              Test 1 = beaker contact                                                                      evaporated at 35 C.      Treated soln, 24                                                                         26n                                                                              13 2.6                                                                              <0.1                             Weight = 13.0 g          Floc (e.g., the flocculated                                                   precipitate)                                         Diluted AMD = 25% AMD + 25 mg/L Cu;                                                                    settled fast                                         DEHPA - peat mix = 1.33 g                                                                              Filtered OK                                          pH = adjusted to 7.0 with 0.38 g Na2CO3                                       Temp = 22 C., Time = 10 & 24 min                                              Solid/Liquid Separation = added 0.22 g paper                                  fiber, stirred + 0.5 mg "PERCOL 351"                           Treatment of AMD with                                                                        Feed soln = AMD + 50 mg/L Cu;                                                                          Settling rate = 15 ft/hr              paper fiber and lime                                                                         1000 ml                  Thickened slurry (1 hr) = 1.6 wt                                              % solids                                             Paper fiber = 0.42 g paper as pulp + sand                                                              Filter rate = 0.8 gpm/sq. ft.                        0.43 g -48 mesh          Cake = 8.56 g moist, 1.62 g dry,                                              19% solids                                           pH = maintained at 9.3 with 0.82 g Ca(OH)2                                    H2O2 = 129 mg                                                                 Temp = 22 C., Time = 10 min                                                   Solid/Liquid Separation = +0.5 mg "PERCOL                                     351" settled and filtered through 7.5 cm                                      towel filter at 2" Hg vacuum                                   Treatment of AMD with                                                                        Feed soln = AMD + 50 mg/L Cu;                                                                          Settling rate = 7.5 ft/hr FINES                                               SUSPENDED                             paper fiber and                                                                              1000 ml                  Thickened slurry (1 hr) = 1.3 wt                                              % solids                              limestone and Na2CO3                                                                         Paper fiber = 0.23 g paper as pulp + limestone                                                         Filter rate = 0.1 gpm/sq. ft.                        0.43 g powder            Cake = 6.28 g moist, 1.32 g dyr,                                              21% solids                                           pH = maintained at 9.0 with 2.25 g Na2CO3                                     H2O2 = 130 mg                                                                 Temp = 22 C., Time = 8 min                                                    Solid/Liquid Separation = +0.5 mg "PERCOL                                     351" settled and filtered through 7.5 cm                                      towel filter at 2" Hg vacuum                                   Treatment of diluted AMD                                                                     Feed soln = 250 ml AMD + 50 mg Cu                                                                      Settling rate = 0.17 ft/min           with Portland cement                                                                         diluted to 1000 ml.      Thickened slurry = 50 ml in 10                                                min                                   without paper fiber                                                                          Paper fiber = none       some fines in suspension                             Portland cement = 0.71 g to pH 8.9                                                                     Filtration = fines passed through                                             filter                                               H2O2 = 30 mg                                                                  pH = maintained at 9.1 with 0.8 mg Ca(OH)2                                    Temp = 23 C., Time = 10 min                                                   Solid/Liquid Separation = added 0.5 mg "PERCOL                                351" to flocculated solids, settled,                                          decanted, and filtered through 7.5 cm                                         paper fiber filter at 1" Hg vacuum                             Treatment of diluted                                                                         Feed soln = 250 ml AMD + 50 mg Cu                                                                      Settling rate = 2 ft/min              AMD with Portland                                                                            diluted to 1000 ml.      Thickening slurry = 50 ml in 10                                               min                                   cement plus paper fiber                                                                      Paper fiber = 0.2 g      clear supernatant solution                           Portland cement = 0.55 g to pH 5.6                                                                     Filtering = 50 ml/8 sec (2.8                                                  gpm/sq. ft.)                                         H2O2 = 30 mg             Precipitate and fiber (pressed):                     pH = maintained at 9.1 with 74 mg Ca(OH)2                                                              thickness = 0.1 mm                                   Temp = 23 C., Time = 10 min                                                                            moist wt = 2.58 g                                    Solid/Liquid Separation = added 0.5 mg "PERCOL                                                         dry wt = 0.77 g, (29.8% solids)                      351" to flocculated solids, settled,                                                                   ignited wt = 0.53 g                                  decanted, and filtered through 7.5 cm                                         paper fiber filter at 1" Hg vacuum,                                           pressed moist cake, dried at 85 C., and                                       ignited at 700 C.                                              Precipitating of Cu,                                                                         Feed soln = 250 ml AMD + 50 mg Cu                                                                      Settling rate = 0.7 ft/min            Zn, Mn, Fe from diluted                                                                      diluted to 1000 ml.      Thickening slurry = 50 ml in 10                                               min                                   AMD with Na2CO3 plus                                                                         Paper fiber = 0.2 g      clear supernatant solution            paper fiber - effect                                                                         H2O2 = 30 mg             Filtering = 65 ml/20 sec (1.1                                                 gpm/sq. ft.)                          on thickening and                                                                            pH = maintained at 9.1 with 0.73 mg Ca(OH)2                                                            Precipitate and fiber (pressed):      filtration     Temp = 23 C., Time = 10 min                                                                            thickness = 0.1 mm                                   Solid/Liquid Separation = added 0.5 mg "PERCOL                                                         vol = 0.7 cc                                         351" to flocculated solids, settled,                                                                   moist wt = 1.83 g                                    decanted, and filtered through 7.5 cm                                                                  dry wt = 0.40 g, (21.9% solids)                      paper fiber filter at 1" Hg vacuum,                                                                    ignited wt = 0.18 g                                  pressed moist cake, dried at 85 C., and                                       ignited at 700 C.                                              Precipitation of Cu,                                                                         Feed soln = 250 ml AMD + 50 mg Cu                                                                      Settling rate = 0.2 ft/min            Zn, Mn, Fe from                                                                              diluted to 1000 ml.      Thickened slurry = 55 ml in 10                                                min                                   diluted AMD with Na2CO3                                                                      Paper fiber = none       supernatant solution contained        without paper fiber -                                                                        H2O2 = 30 mg             suspended fibers                      determine precipitate                                                                        pH = maintained to 9.1 with 0.73 g Na2CO3                                                              Filtration = fines passed through                                             filter                                filterability  Temp = 23 C, Time '2 10 min                                                   Solid/Liquid Separation = added 0.5 mg "PERCOL                                351" to flocculated solids, settled,                                          decanted, and filtered through 7.5 cm                                         paper fiber filter at 1" Hg vacuum                             Precipitation of                                                                             Feed soln = 250 ml AMD + 50 mg Cu                                                                      Settling rate = 0.3 ft/min            Cu, An, Mn, Fe from                                                                          diluted to 1000 ml.      Thickened slurry = 40 ml in 10                                                min                                   diluted AMD with                                                                             Paper fiber = none       supernatant solution contained        Na2CO3 without paper                                                                         H2O2 = 30 mg             suspended fibers                      fiber to determine how                                                                       pH = maintained to 9.1 with 0.73 g Na2CO3                                                              Centrifuged sludge volume = 9 cc      much sludge is formed                                                                        Temp = 23 C, Time '2 10 min                                                   Solid/Liquid Separation = added 0.5 mg "PERCOL                                351" to flocculated solids, settled,                                          decanted, and centrifuged solids at                                           1000 rpm for 5 min                                             "Blank" Test   Feed soln = demineralized water only, 1000                                                             Paper fiber did NOT flocculate        with paper fiber and                                                                         Paper fiber = 0.3 g      Pressed fiber,                        demineralized water                                                                          H2O2 = 10 mg             moist wt = 0.90 g                                    pH = maintained to 9.1 with Na2CO3                                                                     dried wt = 0.25 g                                    Temp = 23 C., Time = 10 min                                                                            ignited wt = <0.002 g                                Solid/Liquid Separation = added 0.5 mg "PERCOL                                351" and filtered through paper fiber.                                        Pressed fiber, dried at 85 C., and                                            ignited at 600-700 C.                                          Precipitate CN from                                                                          Feed soln = 0.5 g/L NaCN Assays (mg/L)                                                                            CN, total                  cyanide solution as                                                                          To 1000 ml soln was added 0.1 g Na2S2O5,                                                               Feed soln  ˜260                 ferric ferrocyanide                                                                          to pH 5, added 0.3 g FeSO4, and adjusted to                                                            Treated soln                                                                             36                         using paper fiber                                                                            8 with NaOH              Flocculated and settled rapidly       as a filter aid                         Filtered well                                                                 Comment: colorless (no blue)                                                  filtrate was                                                                  obtained                              __________________________________________________________________________

While various embodiments of the present invention have been describedin detail, it is apparent that modifications and adaptations of thoseembodiments will occur to those skilled in the art. However, it is to beexpressly understood that such modifications and adaptations are withinthe scope of the present invention, as set forth in the followingclaims.

What is claimed is:
 1. A method for remediation of feed solutionscontaining a metal, comprising:(a) precipitating a metal from a feedsolution comprising acid mine drainage to form a metal precipitate; (b)dispersing discrete fibers in said feed solution to form a productcomprising a fiber and said metal precipitate; and (c) removing saidproduct from said feed solution to form a treated solution and arecovered product containing the metal precipitate.
 2. The method, asclaimed in claim 1, wherein said feed solution is substantially free ofsolids before said precipitating step.
 3. The method, as claimed inclaim 1, wherein said metal is selected from the group consisting ofaluminum, arsenic, beryllium, boron, cadmium, chromium, fluorine,nickel, selenium, vanadium, lithium, molybdenum, barium, lead, mercury,silver, copper, zinc, manganese, iron, compounds thereof and mixturesthereof.
 4. The method, as claimed in claim 1, wherein said feedsolution comprises a stream that has a rate of flow greater than about10 gallons/minute.
 5. The method, as claimed in claim 1, wherein saidmetal has a concentration in said feed solution of less than about 50mg/l.
 6. The method, as claimed in claim 1, wherein said treatedsolution has a concentration of said metal that is less than about 1.0mg/l.
 7. The method, as claimed in claim 1, wherein said precipitate isselected from the group consisting of hydroxides, silicates, sulfides,xanthates, phosphates, carbonates, cellulose-derivatives and mixturesthereof.
 8. The method, as claimed in claim 2, wherein said discretefibers comprise a precipitant to precipitate said metal.
 9. The method,as claimed in claim 2, wherein said precipitant is selected from thegroup consisting of hydroxides, silicates, sulfides, xanthates,phosphates, carbonates, hydroxyethyl cellulose and mixtures thereof. 10.The method, as claimed in claim 1, wherein said removing step comprisesfiltering said feed solution to form said recovered product.
 11. Themethod, as claimed in claim 4, wherein said rate of flow is greater thanabout 500 gallons/minute.
 12. The method, as claimed in claim 1, whereinat least about 95% of said metal precipitate forms a product with saiddiscrete fibers.
 13. The method, as claimed in claim 1, furthercomprising combusting said dewatered wherein the concentration of saiddiscrete fibers in said feed solution is from about 100 to about 500mg/l.
 14. The method, as claimed in claim 4, wherein said rate of flowis greater than about 100 gallons/minute.
 15. The method, as claimed inclaim 1, wherein said recovered product comprises at least about 75% ofsaid metal precipitate in said feed solution.
 16. The method, as claimedin claim 1, wherein said recovered product comprises at least about 85%of said metal precipitate in said feed solution.
 17. The method, asclaimed in claim 1, wherein said dewatered recovered product has aremoved product comprises at least about 90% of said metal precipitatein said feed solution.
 18. The method, as claimed in claim 1, whereinsaid discrete fibers comprise a component selected from the groupconsisting of cellulose, glass, plastic, cotton or wool.
 19. The method,as claimed in claim 1, wherein at least about 75% of said metalprecipitate forms a product with said fibers.
 20. The method, as claimedin claim 1, further comprising:contacting said feed solution with aflocculent after said dispersing step.
 21. The method, as claimed inclaim 1, wherein said precipitating step comprises:contacting said feedsolution with a precipitant, wherein the amount of said precipitantcontacted with said feed solution is at least about 200% of thestoichiometric amount relative to the amount of said metal to be removedfrom said feed solution.
 22. A method to remove a metal from a feedsolution that includes water runoff from a mine, comprising:(a)precipitating said metal from said feed solution to form a metalprecipitate selected from the group consisting of hydroxides, peroxides,silicates, sulfides, xanthates, phosphates, carbonates,cellulose-derivatives and mixtures thereof wherein said metal isselected from the group consisting of aluminum, arsenic, beryllium,boron, cadmium, chromium, fluorine, nickel, selenium, vanadium, lithium,molybdenum, barium, lead, mercury, silver, copper, zinc, manganese,iron, and compounds thereof and mixtures thereof wherein said metal hasa concentration in said feed solution before the precipitation step ofless than 50 mg/l; (b) mixing discrete cellulosic fibers in said feedsolution to form a product comprising a cellulosic fiber and said metalprecipitate; and (c) filtering said product from said feed solution toform a recovered product and a treated solution, wherein theconcentration of said metal in said treated solution is no more thanabout 25% by weight of the metal concentration in said feed solution.23. The method, as claimed in claim 22, wherein said feed solution issubstantially free of solids before said precipitating step.
 24. Themethod, as claimed in claim 22, wherein the concentration of saiddiscrete cellulosic fibers in said feed solution is from about 10 toabout 1,000 mg/l.
 25. The method, as claimed in claim 22, wherein saidmixing step is done in the substantial absence of a flocculent.
 26. Amethod for concentrating a number of different types of metals derivedfrom acid mine drainage and contained in a feed solution comprising:(a)precipitating at least about 75% by weight of said metals from said feedsolution to form a precipitate, said feed solution having a rate of flowgreater than about 10 gallons/minute and a concentration of said metalsof less than about 50 mg/l; (b) dispersing discrete fibers in said feedsolution to form a product comprising a fiber and said precipitate; and(c) removing said product from said feed solution to form a treatedsolution, wherein said metals have a concentration in said treatedsolution that is less than about 75% by weight of the metalsconcentration in said feed solution.